Circuit interrupter



Dec. 8, 1953 s. l. LINDELL ET AL CIRCUIT INTERRUPTER 4 Sheets-Sheet 1 Filed Feb. 27, 1952 Las /lL V Sig Dec. 8, 1953 s. l. LINDELI. ET AL CIRCUIT INTERRUPTER 4 Sheets-Sheet 2 Filed Feb. 27, 1952 Zes/37.5

3 7 ab d )Il k Dec. 8, 1953 S. l. LINDELL ET AL CIRCUIT INTERRUPTER Filed Feb. 27, 1952 4 Sheets-Sheet 4 Patented Dec. 8, 1953 CIRCUIT INTERRUPTER Sigurd I. Lindell, Chicago, and Charles H. Baker, Maywood, Ill., assignors to S & C Electric Company, Chicago, Ill., a. corporation of Delaware Application February 27, 1952, Serial No. 273,638

(Cl. ZOU-120) 18 Claims.

This invention relates, generally, to circuit interrupting apparatus and it has particular relation to fuses for use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery voltage. This application is a continuation-in-part of our abandoned application Serial No. 663,332, filed April 22, 1946, and of our aban cloned application Serial No. 67,182, filed December 24, 1948.

Certain embodiments of the invention disclosed herein were designed particularly for use in connection with a system operating at 115 kv. and are intended for interrupting, not only relatively low fault currents, but also for interrupting short circuit currents on a power system operating at this voltage, the current interrupter being connected directly in the high voltage circuit and being required to withstand not only the normal frequency recovery voltage but also the transient recovery voltage. It will be under-- stood that the normal frequency recovery voltage is the normal frequency R. M, S. voltage impressed upon the current interrupter after the current has been interrupted and after high frequency transients have subsided. The transient recovery voltage, which may be substantially greater than the normal frequency recovery voltage, is the transient voltage which occurs across the terminals of the current interrupter at the time of are extinction. Where two or more circuit interrupters of the fuse type are employed in a three phase circuit, the transient recovery voltage is generally considered to be the voltage applied across the rst fuse to clear.

When fuses are employed at the higher system voltages on the primary side of large transformer banks and secondary faults occur, they may be required to interrupt low power factor currents of relatively low magnitude under conditions that produce such high normal frequency and transient recovery voltages that conventional fuses flashover between the line terminals. This is particularly true when the primary side of the transformer bank is delta connected or Y-connected with ungrounded neutral. Under such conditions the melting time of the individual fuses of an installation is relatively long and a slight difference in melting characteristics may be sufcient for one fuse to blow ahead of another and attempt to interrupt the low fault current at phase to phase normal frequency system voltage instead of at phase to ground voltage.

When a fuse blows and while the are is being extinguished, the dielectric strength momentarily established in the interrupting channel at current zero may rise above the rod gap value of the external parallel paths of the same length through still air. A transient recovery voltage may be created and sustained by the arc space sufficient to produce ashover along these parallel paths. In the fuse of the type disclosed in Triplett Patent No. 2,379,200, issued June 25, 1945, which is a solid material type of fuse, and in liquid fuses of the type disclosed in Conrad Patent No. 2,091,431, issued August 31, 1937, the line terminal or ferrule away from which the arc is drawn acts like one rod gap terminal which is paired with the rod-like terminal which moves away therefrom to extend and extinguish the arc. When the voltage between these terminals reaches a value such as to produce a critical gradient in the air adjacent the line terminal or ferrule, streamers are created from the line terminals and breakdown may proceedby propagation through the air to the moving terminal or to the other line terminal or ferrule at the opposite end of the fuse tube at a voltage no higher than the rod gap value of the distance between the first mentioned line terminal and the moving rod-like terminal. Thus even though the interrupting channel of the fuses of the types referred to may possess the ability satisfactorily to interrupt the circuit, in so far as the fault current and recovery voltage are concerned, under certain severe circuit conditions arc over may occur outside of the interrupting channel through the air which will cause ashover of the line terminals. It has been found that this has been caused, in part, by ineiiicient arrangement of the insulation of the fuse housing and because of insufficient spacing between the line terminals when full consideration is given to not only the normal frequency recovery voltage but also to the transient recovery voltage.

While a solution to the problem thus presented has been worked out in connection with a fuse designed for use with a kv. system, it will be understood that the fuse in which are incorporated the various features of the present invention is not limited to this particular voltage. By suitable and appropriate changes in design, the present invention can be employed in the construction of fuses designed to operate on systems energized at higher or lower voltages. For example, the present invention can be embodied in fuses intended for use on systems operating at 34.5 kv., 46 kv., 69 kv., 92 kv., and 138 kv. More over, it will be understood that the present invention may be adapted for use in systems op- 3 erating at voltages other than these specifically enumerated and be employed in circuit inn terrupters of the separable contact type as well as of the fuse type.

The object o1" the present invention, generally stated, is to provide circuit interrupting appa ratus of the high voltage type which shall be simple and enicient in operation and which may be readily and economically manufactured and installed.

Another object is to so proportion the conduct` ing and dielectric components of a high voltage circuit interruptor that the dielectric break-down value along any path in para] with theI interrupting channel. will exceed. the dielectric strength of the interrupting channel at any' time during or immediately following operation of the fuse so that any restrilring of the arc during the interrupting shortly thereafter as a result o reilected voltage surges or prolonged transient recovery voltag will take place in the bore of the arc passageway and will not talee place either through the air outside oithe fuse tuhe between line terminals or along the inner surface or" the :i tube between it and the iilling of solid .guishing material which provides the bore from the surlace of which on arc extinguishing inedn evolved to assist in extinguishing the arc.

' A further object is to extend witl'iin the in ate ing circuit interruptor housing, such a [use tube, the line terminal away Troni which the rodlike terminal moves on drawing arc for substantial distance so as to prevent the torino n of a critical gradient air adjacent the ter minal during the operation of the interrupt-er and to provide in a structure of this type ddectric breakdown along any path outside ol the int rupting channel substantially equal to the flashover value of a rod gap oi the same spacing as the external line terminals.

Still another object is to increase the resistance of a tubular circuit interi-unter housing to burst-- ing pressure along the portion thereoie within which the arc is drawn and extinguished.

Another object is to mold the solid arc eatin-- guishing material, such as boric acid, magnesium berate and the like, in the Afuse tube under p s s're so as to provide intimate contact with the surrounding fuse tube and reduce the likelihood of the arc restriling along the juncture oi the solid arc extinguishing material and the surrounding fuse tube.

A still further object of the invention is to pro vide a devious path along the juncture betwc n the solid arc extinguishing material and the si rounding fuse tube by grooving the latter, by

threading the saine, the threads being flattened at the top and bottoni so as to avoid sharp changes in direction of the adjoining surfaces.

Still another obgect of the invention is to re force the 'fuse tube by providing the same w; fibre liner which is arranged to receive the of solid arc extinguishing material.

Another important object of this invention is to 4so proportion the conducting and dielectric coinponents of a high voltage switch'of the separable Contact type that the dielectric breakdown value along any path in parallel with the interrupting channel will exceed the dielectric strength of the interrupting channel 'at any time during or in;- mediately following operation of the switch and separation of its contacts so that` any restri of the arc during the interrupting process, or shortly thereafter, as a result of reflected voltage surges or prolonged transient recovery voltage, will take place in the bore of the arc passageway and will not take place either through the air outside or" the interrupter housing between the external line terminals or along the inner surface of the housing between it and the lining or arc extinguishingl material which provides the bore from the surface of which an arc extinguishing medium is evolved to assist in extinguishing the arc.

Another important object of this invention is to extend within the insulating housing the line terminal away from which the movable contact moves on drawing of the arc for a substantial distance .so as to prevent the formation of a critical gradient in air adjacent this line terminal during the operation oi"- the switch and drawing of the arc and to ppvide in a structure of this typea dielectric breakdown value along any path outside of the interI '-,p ing channel substantially equal to the iiashover value of red gap of the saine spacing as the external line terminals and substantially greater than the breakdown value between the fixed and movable arcing terminals or contacts at any during or ter arc current interruption.

Still another object of this invention is to construct the insulating housing which is coextensive with the arc passageway therein and extensions from the line lals as to be iree from voids so that the dielectric around the passageway and extensions is composed of insulating material other than air.

Other objects of the invention will, in part, be obvious and in part a ear hereinafter.

The invention is .losed in the embodiments thereof shown the accompanying drawings and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the constructions set forth hereinafter and the scope of the application of which will be indice in the appended claims.

For a more complete understanding of the nature and scope oi this invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

Figure l is a view, in side elevation, of a fuse construction in which the present invention is incorporated;

Figures 2A-2B2C, taken together, show` a longitudinal sectional View through the fuse tune construction of Figure l, the fuse being shown in the unblown condition;

Figures 23A-3B are Views similar to Figures 2A-2B, but showing the fuse in the blown condition;

Figure 4 is a detail sectional View, at an enlarged scale, showing how the solid arc extinguishing material is molded into grooves or threads on vthe inner surface of the ruse tube;

Figure 5 is a detail sectional View illustrating a modified form of the invention in which the fuse tube is provided with a reenforcing nbre liner;

Figure 6 is a longitudinal sectional view of a circuit interrupting device of the separable contact or switch type constructed in accordance with this invention, the switch being shown in the closed position; and

Figure 7 is a view, similar to Figure 6, but showing the switch in the open circuit position.

Referring nowiparticularly to Figure 1 ofc the drawings, it will be observed that the reference character Il] designates an insulating tube which accanto forms'the housing for the circuit interrupter of the fu's'e type to be described in detail hereinafter. At its opposite ends the insulating tube IIJ is provided with external or line terminals II and I2 which are arranged to have contact engagement with suitable terminal clips as is more fully set forth in Lindell Patent No. 2,484,839, issued October 18, 1949. However, it will be understood that any suitable form of terminal clip can be employed in practicing the present invention and that the particular form of terminal clip disclosed in the patent of Lindell, just referred to, is mentioned solely for illustrative purposes. The terminals II and i2 are formed of suitable conducting material such as brass.

As disclosed more fully in the copending application of Sigurd I. Lindell, Serial No. 663,832, led April 22, 1946, the fuse construction herein disclosed is arranged to be mounted so that, when the fuse blows, it will automatically move under the influence of gravity and the biasing force of the contact clips to a position where a relatively large air gap is provided between the upper line terminal II and the associated terminal clip which is connected to the circuit. 1n order to provide such operation the fuse has a latch tube I3 which is secured at its lower end to a latch release flange I4 that, together with the tube I3, is arranged to be moved upwardly ln a manner to be described hereinafter for the purpose of unlatching the locking mechanism and permitting the fuse to fall or drop out to the open circuit position.

The fuse is arranged to exhaust downwardly f on operation thereof through the lower line terminal I2. In order to cool and con-dense the arc products and limit the escape of flame from the lower end of the fuse, a condenser assembly may be provided on the lower line terminal I2. Its shell is indicated at I6. The internal details of construction of the condenser will be set forth more fully hereinafter.

Particular reference will now be made to Figure 2B. As there shown, the fuse tube Ill is formed of insulating material. This may be a phenolic condensation product, such as Bakelite or it may be a melamine tube. The tube I0 may be a solid rolled phenolic condensation product tube and may have a baked coating of melamine enamel on the outside and the inside to provide weather and arc resisting surfaces superior in these respects to the surface of the tube itself.

At the central portion of the tube Ill its inn ternal diameter is reduced as indicated at I8 for the purpose of providing a section which has increased resistance to bursting pressure, it being understood that relatively high pressures may be generated within the tube I0 in the portion thereof where the arc is drawn and extinguished. This configuration also aids in more uniformly distributing the dielectric flux in the air about the ends of the terminals embedded therein. The thickness of the tube wall should be such as to withstand without puncture one half of the normal frequency voltage.

With a View to providing an arcing passageway from whose surface an arc extinguishing medium can be evolved, cakes I9 of solid arc extinguishing material are positioned along the bore of the reduced diameter section I8. These cakes I9 are annular in form and when placed one above the other provide a continuous bore in which the arc may be drawn and extinguished. Various solid arc extinguishing materials may be em- 6 ployed. For example, boric acid or magnesium borate 'may be used.

As indicated hereinbefore, difficulty has been encountered in failure of the fuse by improper operation as a result of arcing over along the Juxtaposed surfaces of the tube Ill and of the solid arc extinguishing material I9. It is believed that this has been caused by imperfections in the bond between the two materials which had been attempted by the use of a dielectric cement. This difficulty has been overcome in accordance with the present invention.

As shown more clearly in Figure 4 of the drawings, the inner surface of the thickened portion l 8 of the wall of the tube ID is grooved by threading the same as indicated at 2I. However, care is taken not to provide sharp points and valleys on and between the threads 2l by flattening the inner edges thereof as indicated at 22 and also providing flat surfaces 23 between the adjacent threads 2 I. This construction provides a devious, roundabout or indirect path along the juxtaposed surfaces of the two materials which is substantially greater (at least forty per cent greater) than the total length of the stack of cakes i9 of solid arc extinguishing material.

Another important feature of the present invention is the manner in which the cakes I9 of solid arc extinguishing material are placed in the fuse tube l0. `initially their outer diameter is such to permit their being readily placed within the threaded bore of the enlarged section it' of the tube lc around an arbor. Thereafter the calres are successively subjected to a molding pressure of approximately 4000 pounds per square inch by a hollow ram as a result of which the solid material is rmly compacted in place in and between the threads 2i. Thereafter the arbor is withdrawn, leaving the bore 20 which forms the arc passageway.

The melamine coating over the threads 2l provides an arc resisting surface which reduces the likelihood of dash-over therealong as might be the case if such a protection covering over the surface of the phenolic condensation product were not used.

At each end of the column of cakes I8 of solid arc extinguishing material there is provided a reenforcing ring of suitable insulating material such as fibre. One of these is indicated at 21 at the upper end in Figure 2B and the other is indicated at 28 at the lower end. The reenfcrcing ring is flared outwardly to facilitate the outward flow of the products of the arc, as will be readily understood.

Movably mounted within the bore in the cakes l@ of solid arc extinguishing material and substantially filling the same is a rod-like terminal 29. At its upper end the terminal 20 is provided with a contact tip 35i 4which is arranged to be engaged by Contact fingers 3i the upper ends of which are turned inwardly and biased inwardly by a garter spring d2. The contact fingers di extend upwardly from a contact fitting $3 which, in part, serves to hold the reenforcing ring 2'! in place.

An electrical connection between the line terminal li and the contact fingers 3l is provided by a conducting tube or terminal extension 34 of brass, copper, copper alloy or other suitable conducting metal. It will be noted that the lower end of the conducting tube 34 is threaded onto the Contact fitting 33 and that a nut '35 is threaded onto the upper end thereof and also is threaded into the line terminal II thereby forming an extension thereof. This is shown in Figure 2A. A loci; nut 35 serves to hold the contact nut 35 in place.

As will hereinafter appear, when the fuse blows, it is desired that the rod-like terminal 129 be moved rapidly through the bore 20 in order to extend the arc therein and permit the heat thereof to evolve an arc extinguishing medium, such as water vapor, from the bore so as to deionize the arc space and assist in extinguishing the are. For this purpose a helical compression spring 31 is located within the conductor tube 34 and bears against the iitting 33 and the under side of a spring seat 3B which is secured to the lower end of a compression tube 39 which may be formed of brass. The compression tube 39 carries a base 4i) at its upper end from `which a stud 42 depenr s. On opposite sides of the lower end of the stud 42 links 43 (only one of which is shown) are pivoted by a pin 44. Between the links 43 a pulley 45 is rotatably mounted on a pin or shaft 46.

A cable connector assembly, shown generally at 49, extends over the pulley 45 and provides both mechanical and electrical connection to the rod-like terminal 29 for effecting retraction thereof and also for maintaining electrical circuit connection thereto while it is moving 'through the bore 2U and after the contact tip 39 has moved away from the contact fingers 3l.

The cable connector assembly 49 comprises a core 50 formed of a large number oi strands of relatively fine wire, such as copper wire and an outer sheath 5I formed by a closely wound coil spring preferably of stainless steel. One end of the cable connector assembly 49 is connected to the contact tip of the rod-like terminal 29, shown in Figure 2B, while the other end is con nected to a strap or cable link 52. The lower end of the strap or link 52 is secured, as by rivets 53 to the contact lltting 33.

When the fuse blows, as will be described herenafter, the spring 31 is released and it moves the compression tube 39 upwardly, carrying with it the pulley 45. Because of the mechanical arrangement thus provided, the rod-like terminal 29 moves at twice the speed that the compression tube 39 is moved and its extent of movement is twice as great. The compression tube 39 carries with it the base 4I) which moves upwardly until it engages a cap 54 which is secured to the upper end of the latch tube I3. As set forth hereinbefore, the upward movement of the latch tube I3 lifts therewith the flange I4, as shown in Figure 3A, to eiect unlatching of the fuse so as to permit it to drop out. The latch tube I3 moves upwardly until a shoulder 55, Figure 2B, on the spring seat 38 engages a shoulder 56, Figure 2A, on the inside of a stop tube 51 which is secured to a fitting 58 that forms part of the fuse mounting contact mechanism which is described in more detail in Lindell Patent No. 2,434,839, issued October 18, 1949. The stop tube 51 is held in place in the fitting 5B, in part, by a sleeve 59 over which the lower end of the tube 51 is rolled and which bears against the under side of the fitting 58. The latch tube I3 is held in the position shown in Figure 2A of the drawings by a coil compression spring B2 which is located between the tubes I3 and 51 and at its lower end bears against the upper end of a tubular extension G3 from the flange I4 and at its upper end against the underside of a collar 64 which is secured to the upper end of the stop tube 51.

The fitting 58 has integrally formed ears 65 and 66 on opposite sides between which links are pivoted to provide for contact engagement between the line terminal II and the cooperating fuse clip. The details of construction are more fully set forth in the Lindell patent last referred to. As shown in Figure 2A the upper line terminal II is secured to the upper end of the tube I9 by suitable screws 61, two of which are there illustrated.

As indicated hereinbefore, diiculty has been encountered in fuses of the prior art in flashover of the fuse tube from or to the line terminal away from which the movable terminal is withdrawn. It is believed that this has been caused by the overstressing of the air immediately adjacent the end of the line terminal nearer to the movable terminal after it has been moved to extend the are away from the line terminal, on operation of the fuse.

With a view to relieving this condition and providing a more efiicient design, the line terminal I2 is extended by an exhaust tube 10 of suitable conducting material, such as brass while, of course, retaining the conducting tube 34. As i1- .f lustrated in Figures 21B-2C, the exhaust tube or terminal extension 10 is positioned inside of the tube I0 at its lower end and extends upwardly. The inturned upper end bears against the fibre retaining ring 2B and serves to hold the same in place. At its lower end the tube 10 is connected to the lower line terminal I2 by a nut 1I which, as shown in Figure 2C, is threaded to the lower end of the tube 10 and also is threaded into the line terminal I2. A lock nut 12 serves to hold the nut 1I in place.

Near its upper end the exaust tube 10 carries a narrow bridge or fuse element support 13 from which a rod-like terminal 14 extends upwardly. A tubular adapter 15 and nuts 16 cooperate to hold the terminal 14 in place on the bridge 13 and to provide good electrical and mechanical com nection therewith. The terminal 14 is connected to the rod-like terminal 29 by a coiled fusible element 11, preferably of silver, and a strain element 18, preferably a high strength alloy wire, such as Nichrome or Chromel wire. It will be understood that the bridge 13 is securely fastened to the exhaust tube 10 so that it makes proper mechanical and electrical connection therewith.

As shown in Figure 2C, the lower line terminal I2 may be secured to the lower end of the tube I0 by suitable screws 8l. two of which are shown.

It will be apparent that the conducting tube 34 and the tapered tting 33 perform at their end of the tube I0 the same function as does the exhaust tube 1I) with its tapered end at its end of the tube I0 in more uniformly distributing the dielectric stress during and after circuit interruption.

In order to mount the condenser shell I6 a reducer fitting 82 is threaded into the lower end of the lower line terminal I2 and the shell I Ii is threaded thereon, as illustrated in Figure Within the condenser shell I6 is a condenser 93 0f the type shown in Triplett Patent No. 2,379,200, issued June 26, 19.45, which serves to cool or oondense the products of the arc resulting from Vthe blowing of the fusible and strain elements 11 and 18 as will be readily understood.

It is desirable that the condenser shell I6 be closed to the atmosphere except when the fuse blows. This prevents the introduction of extraneous matter into the interior of the fuse. For this purpose a valve seat 84 is threaded vinto the lower end of the condenser shell I6 and a valve cover 85 is arranged to cooperate therewith. The valve cover 85 is slidably mounted on the valve seat 84 by a stud 86 and is held in the closed position by a coil compression spring 81 which reacts between the upper surface of the valve seat 84 and a nut 88 at the upper end of the stud 88. When sufficient pressure is generated within the condenser shell le on the blowing of the fuse, the arc products expand through apertures 89 in the valve seat Bti, lift the valve seat 84 and are exhausted into the atmosphere.

Instead of forming the tube i o with the central portion I3 of reduced diameter, as shown in Figure 2B, a liner may be provided for accomplishing the same purpose of reenforcing the tube at this point. As shown in Figure 5, a tube l', similar to the tube lll, but having a uniform bore throughout, may be used together with a liner 9| of horn bre or similar material, such as Bakelized horn fibre. Preferably, the liner 9| is first formed and then the tube I0 of Bakelite or melamine is formed therearound under heat and pressure. fin insulating resin, such as melamine, serves to bond the liner 3l in place in the tube IIJ when the latter is formed of material such as Bakelite The inner bore of the liner 9i may then be grooved, as described hereinbefore and illustrated in Figure 4, for receiving the cakes I9 of solid arc extinguishing material which may be molded or compacted therein to provide the Y required structure. The bre liner acts not only to absorb the shock of the high pressure created by high current arcs but also in conjunction with the arc extinguishing material I9 serves to extinguish any incipient arc appearing along the adjoining surfaces thereof.

With a view to indicating the order of the dimensions employed in constructing the fuse shown in the drawings and described hereinbefore, reference will now be made to the general dimensions of the various parts thereof.

As indicated hereinbefore, the fuse disclosed herein is designed particularly for use with a system operating at 115 kv. However, the principles of construction can be used for voltages other than this and the specic dimensions to be referred to hereinafter are to be considered only for illustrative purposes. v

The fuse tube iii or lil may be about fifty-two inches long and have an outside diameter vof about three inches. The internal diameter of the tube Ei or lil' at the ends is about 1% inches while the internal diameter of the bore for receiving the cakes l!! of solid arc extinguishing material may be inches. The threads 22 may be formed by a one inch pipe thread tap which is ground to provide the desired contour of the threads, described. The rod-like terminal 29 is about twenty-seven inches long and is arranged to have a travel of about twenty-two inches from the position shown in Figure 2B to the position shown in Figure 3B. When the rod-like terminal iii) is in the retracted position, shown in Figure 3B, it extends into the tube i@ about .fifteen inches from the upper end thereof. The exhaust tube 'iii extends into the lower end of the tube IS for about fifteen inches with the result a gap of about twenty-two inches in length is provided within the bore 2i), substantially midway between the ends of the line terminals il and l2 each of which is coextensive with its end of the fuse tube for about two inches'. This relationship is illustrated by the broken lines in Figure l.

.It will be apparent from the foregoing data iii that the length of the interrupting channel in the bore 20 is approximately equal to the sum of the lengths of the extensions from the line terminals li and i2, i. e., twenty-two inches for the interrupting channel and twenty-eight inches for the sum of the lengths of the extensions from the line terminals I i and I2 measured from their nearer ends. The minimum wall thickness of the tube Il] at the inner ends of the embedded extensions 3ft and l@ of the terminals Ii and i2 is such that its dielectric strength is equal to at least half of the ilashover value from one terminal Il to the other terminal I 2 or, as indicated hereinbefore, is capable of withstanding without puncture one-half of the normal frequency voltage so as to prevent puncture of the tube walls and completion of breakdown from one terminal extension to the other in air if a critical gradient is approached in the air outside of the bore 2i).

The wall thickness and diameter of the tube ill are important also in controlling the dielectric stress in the air outside of the tube adjacent the ends of the rod-like terminal 2Q and the tube 'lil when the former is in the blown position as illustrated in Figure 3B. These dimensions are chosen and the ends are shaped so as to allow the stress lines emerging from the terminal extensions 34 and 'iii to diverge appreciably before entering the air. Thereby the voltage gradient in the surrounding air is lowered. It would be impractical to employ such a thickness of solid insulation for the tube lll as would materially reduce the total voltage imposed on the air. The terminal extensions 3l! and 1i), which may be considered as embedded terminals, are shielded by the solid dielectric material making up the tube I0. With respect to the outside air around the tube iii these embedded terminals fall into a class between rod gaps and sphere gaps. These embedded terminals 34 and 10 also tend to shield the corners of the line terminals Il and l2 and to reduce the stress along the coextensive surface of the tube I0. The net result of the complete structure with the proportions indicated is that the breakdown strength along any gap involving the air outside of the tube I3 and between any two of the terminals is raised to a level considerably above the rod gap value 1, for the same distance.

The potential existing between the terminal extension 34 and the rod-like terminal 29 at the upper end of the tube I0 and the terminal ex-- vious path over the juxtaposed threaded exterior` surface of the arc extinguishing material I9 and interior surface of the tube IS, Figure 4, or interior surface of' the fibre liner 9i, Figure 5. Since this devious path between the conducting parts at its ends is substantially greater in length than the path through the bore 2t, any voltage break down that takes place always will occur in the latter and not in the former. If such a devious path were not provided and the arc extinguishing material I@ were assembled having a path over. its exterior surface about equal in length to the length of the bore 2D, this is the likelihood that arcing vwill take place over this exterior surface rather than through the bore 2G when the conducting parts at the ends of these parallel paths are subjected to high potentials that may arise for various reasons. lf such arcing over the exterior surface should occur, thev circuit may not be properly cleared and the interrupter may fail thereby requiring other means in the circuit to interrupt the current flow.

While the present invention has been described particularly in conjunction with a fuse of the solid arc extinguishing material type, it will be apparent that it is applicable to other types of circuit interrupters, such as those which include separable contacts between which an arc is drawn. Also, it may be used in a fuse of the liquid type such as disclosed in Conrad Patent No. 2,091,431, issued August 31, 1937.

Referring now particularly to Figures 6 and 'l of the drawings, it will be observed that the reference character I I designates, generally, a switch or circuit interrupter of the general type shown in Lindell et al. Patent No. 2,351,826, issued June 24, i944, and constructed in accordance with this invention. The switch or circuit interrupter may be employed separately or it may be employed in conjunction with the disconnecting switch blade or switch construction shown in this patent or in apV lication Serial No. 41,597, filed July 30, 1948. Since the present invention is directed particularly to the features of construction of the switch IIG, the operating mechanism therefor will not be described in detail herein other than to point out a certain portion of the same for illustrative purposes.

The switch or circuit interrupter IIII includes a pair of line terminals III and II2. `It will be recognized that the line terminal I I I may be connected to the stationary contact of the disconnecting switch shown in the aforesaid Lindell et al. patent while the line terminal |I2 is arranged to have sliding or wiping contact engagement with a flexible contact member carried by the switch blade. The line terminal I I2 also serves as a housing lfor a portion of the operating mechanism which will be referred to in more detail hereinafter. However, it will be understood that the line terminals III and II2 may constitute conventional line terminals of a switch when the switch or circuit interrupter I||| is employed by itself. A portion of the operating mechanism that can be employed in conjunction with the switch I I0 is illustrated, generally, at I3 within the housing I I2.

The line terminals II I and II2 are held in insulated spaced relation by an insulating housing that is indicated, generally, at I4. As shown, the construction is such that the line terminals III and ||2 do not overlap the outer surface of the insulating housing I i4. n

It will be observed that the insulating housing is tubular in form and that it may be formed by a tube |I5 of insulating material. The insulating material for the tube ||5 preferably is weatherproof, and for this purpose a phenolic condensation product, or melamine may be employed. Also, with proper rearrangement of the parts, the tube I I5 may be formed of porcelain.

The tube I5 has 4a central bore I I5 the length of which is equal to about one half the length of the tube I I5 and it is placed midway between its ends. Within the bore ||6 there is. a stack of fibre washers ||1 which together provide a bore IIB that forms an arc passageway between the line terminals I II and I|2 in which the arc incident to the operation of the switch |10 is drawn and extinguished. The nbre washers ||1 vpreferably have a press fit with the bore I I6 and a suitable cement is provided for holding them in place. While the stack of fibre washers is illustrated as being .employed to provide the arc passageway ||8 from whose surface an are extinguishing medium is evolved when it is subjected to the heat of the arc, it will be understood that other materials, such as boric acid and magnesium berate can be employed. If the tube ||5 is formed of insulating material, such as melamine, which inherently has arc extinguishing properties, then the stack of fibre washers |I1 can be omitted and the arc passageway or bore |I8 provided in the tube |I5 itself.

The end portions of the tubular insulating housing II5, when it is formed of a resin, such as those referred to above, have threaded bores |2| and |22 the diameter of which is greater than the diameter of the bore IIIS. The inner ,5 surfaces |23 and |24 of each of the threaded bores I2| and |22 is tapered toward the ends of the bores I I6. The purpose of this configuration will be apparent presently.

Each of the line terminals III and I I2 is provided with a tubular extension |25 and |25, re-

spectively, of conducting material. The extensions and |25 project into the housing ||5 for substantial. distances. Preferably the sum of their lengths is vabout equal to the length of the 5 bore ||8 and the extensions |25 and |26 are of equal length. The inner ends |21 and |28 of these extensions |25 and |25 aie tapered to conform to the tapered surfaces |23 and |24 at the inner ends of the threaded bores I2| and |22. The

purpose of this tapered conguration is to aid in distributing substantially uniformly the electrostatic stress in the housing and in the outside air which is incident to the drawing of an arc within the bore I |8 and its extinguishment. This distribution of electrostatic stress is aided by having the insulating housing ||4, which is coextensive with the bore IIB and the tubular extensions |25 and |26 of'sufiicient wall thickness and free from voids so that the dielectric therearound is composed solely of insulating material other than air. There is then no likelihood of the insulation being severely stressed as may be the case under certain operating conditions if there were voids left in the insulating housing I I4, the

voids being filled by air.

It will be observed that the tubular extensions |25 and |26 are externally threaded so that they can be screwed into the threaded bores I2I and |22. In addition the line terminal I I I is threaded onto the extension |25. The extension |25 may be formed integrally with the line terminal II2 as shown. Suitable gaskets |29 and |30 are provided at the ends ofthe insulating housing ||4 to provide a weathertight construction.

Within the bore IIB and tubular extension |26 S there is positioned a movable rod-like contact member |33 the upper end |34 of which is hollow and split to provide flexibility and contact surfaces |35 are provided thereon for contact engagement with a cylindrical contact surface |36 `at the lower end of the tubular extension |25. The diameter of the contact surface |35 is the same as the diameter of the bore |I8 and, in effect, constitutes a continuation thereof. The tubular extension |25 has a large diameter bore |31 therein for the purpose of facilitating the escape of the products of the arc which are the result of its heat and which are principally in the form of metal vapor and gas, the latter resulting from the evolution of arc extinguishing material 15 scoped therein. The rod |38 is rockably mounted 13 near its lower end by a pin |39 which extends through the contact member |33. The rod |38 1S provided for connection to a trailer or follower |40 of insulating material. The trailer tollower Idil is formed of material which evolves an arc extinguishing medium when it is subjected to the heat of the arc. For example, it may be formed of methyl methacrylate resin. if desired, the trailer or follower Ifill maybe formed of other similar insulating material such iibre, melamine, etc. It will be understood that the trailer or follower |48 is drawn into the bore IIS along with the rod-like contact member |33. When the switch 01' circuit interrupter Iii is operated under load, an arc is drawn between the Contact surfaces |35 at the upper end of the rod-like contact member |33 and the contact surface 36 at the lower end of the tubular extension |25. Since the trailer or follower lili? of insulating material is drawn into the bore i Iii, as shown in Figure '7, the arc thus formed is conned between the outer surface of the trailer or follower Elli) and the inner surface of the stack of libre washers II? or the bore IIS. The arc thus coniined is quickly extinguished.

It will be observed that there is a path between the tubular extensions |25 and |25 along the juxtaposed surfaces of the tube I I 5 and the stack of fibre washers I I'I which is parallel to and coextensive with the path therebetween through the arc passageway II. Under certain operating conditions these paths are subjected to high potential stress because or" the voltage that is applied to the extensions I and its. Further, the trailer I4@ as shown in Figure 7 auginents this high potential stress since it substantially fills the arc passageway IIs and thus reduces the space which the arc can occupy. It is for these reasons that it is desirable that the dielectric around the arc passageway il@ and the extensions E25 and |25 be free from voids and for this purpose the stack of fibre washers i I 'i has a press ilt with the bore I i5 in the tube l I5 and is cemented into place. This construction insures that any arc formed between the line terminals Il! and I i2 will be drawn in the bore lili and not along the parallel path between the tube |55 and stack of nbre washers l Il.

It will be understood that any suitable means can be employed for moving the rod-like contact member |33 into and out of engagement with the tubular extension |25. For example, the operating mechanism I i3, referred to above can be einployed. This mechanism includes a lever E43 which is pivoted at |514 to the lower end oi the movable 1'od.-lilre contact 33. At other end the lever |43 is pivoted at Idil to a link |413 which, as shown, is pivoted at Ml to a web MS that may be formed integrally with the lower line terminal I E2. lThe link ille has an integrally formed foot portion i di? which serves as a stop to limit the movement of the Contact member 33 in closing or opening directions. Intermediate the ends of the lever I i3 at l5@ an arm I5! is pitcted for operating the linkage to move the Contact member |33 into and out of engagement with the extension |25. The arm 55 is fastened to a shaft |52 which extends transversely of the line terminal. I2 and has detente at its ends, one of which is illustrated at IEE. lt will be understood that the detente I 53 are arranged to be operated by suitable means, such as by cams on the disconnecting switch blade for rocking the shaft |52 to shift the arm from the position shown in Figure 6 to the position shown in Figure 7. A coil tension spring |54 is strained between the pivot point |45 and the shaft |52 to provide an overcenter toggle linkage and to hold the con tact member |33 in the closed position shown in Figure S or in the open position shown in Figure 7.

Since further changes can be made in the foregoing constructions and different embodiments of the invention can be made without departing from the spirit and scope thereof, it is intended that all matter shown in the accompanying drawings and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

1. In a high voltage circuit interruptor for use with electric power systems wherein the transieht recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube having an arcing passageway substantially egual length to half the tube length located substantially midway its ends, the inner surface ci said tube coextensive with said arcing passageway being threaded, a iilling of arc extingnia ng material having its external surface threaded and interlccked with said inner said tube where by a devious path is provided therebetween having a bore forming said arcing passageway, external terminals at the ends ci tube for connection to the circuit and between which said recovery voltages are applied a stationary metallic extension from each oi iid terminals inside tube extending to the adjacent of said arc-ing passageway for distances substantially beyond any part of the associated external terminal, and means for drawing an in said passageway on operation of the interruptor, ma tallic extensions acting to distribute electrostatic stress at locations substantially one fourth the length of said tube from each end interruption of current iiow therethrough applying voltage stress to the ends of said devious path which because of its greater length compared to the length of said arcing passageway and the extinguishing material threaded int-e tube has a higher voltage break down strength than does said arcing passageway and insurii that any restriking of an arc between said ter: inals will occur in said arcing passageway and not along a path between the former and external to the latter.

2. In a high voltage fuse for use with electric power systems wherein the transient recovery voltage may be substantially greater the normal frequency recovery voltage, in combination, an insulating tube with inter al portion for substantially hallr its length oi reduced diameter to provide increased wall thickness for strengthening the tube at this sec .ion

and having its inner surface threaded, a ii of arc extinguishing material having its externa surface threaded and interlocked with inner surface of said reduced diameter section and having a bore from the surface of which arc extinguishing medium evolved clue to the heat of an are, said threaded inner surface of said reduced diameter portion and arc extinguishing material inter-locked therewith providing a devious path therebetween having substantially greater creepage distance over the juxtaposed surfaces than is provided over the surface of said bore, line terminals at the ends ci said tube for connection to the circuit between which said recovery voltages are applied, a rode like terminal movable through said bore, conmeans biasing said rod-lil e term... one fline terminal, Athe arcing end ci terminal in the retracted 'position said bore near one end thereof, station ducting means extending from the other line Vterminal toward said bore for a distance 4several times the length that said other terminal is coextensive with said tube, and fusible means in terconnecting said roddike terminal and the last mentioned conducting means and holding the former against .the retractne force said spring means until the saine blows on the occurrence of a predetermined overload in the circuit in wl h the fuse connected, said reddike terminal after release and said conducting means apply" volt age stress to the ends of said devious path which because of its greater length as compared to the length of said bore and the arc extinguishing material threaded into tube has a higher voltage "breal: down strength than said bere.

3. In a high voltage fuse for use with electric power systems wherein the transient recovery voltage may be substantially greater normal frequency recovery voltage, in combination, an insulating tube with the internal cenu tral portion for substantially half its ength of reduced diameter to provide increased wall th y. ness for strengthening the tube at this the inner surface of said reduced diameter tion being grooved, a filling et are eirtinguis ing material compacted into said grooves whereby the voltage breakdown strength along the devious path thus provided between said tube and said arc extinguishing material substantie that over the exterior surface of the e between its ends, said iilling oi are material having a central bore from the su ace of which an are extinguishing medium is evolved due to the heat of an arc, line terminals at the ends of said tube for connection to the circuit and between which said recovery voltages are applied, a reddito terminal movable through said bore, conducting means interconnecting rod-lilre terminal and one of said line terminals, spring means biasing said rod-like terminal toward said one line terminal, the arcing end of said rod-lihe terminal in the retracted position remaining in said bore near one end thereof, conducting means extending from the other line terminal toward said bore for a distance several times the length that said other terminal is coextensive with said tube, and fusible means interconnecting said rodlike terminal and the last mentioned conducting means and holding the former against the retractile force of said spring means until the same blows on the occurrence of a predetermined overload in the circuit in which the fuse is connected.

4. In a high voltage fuse for use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube with the internal cen tral portion for substantially half its length of reduced diameter to provide increased wall thickness for strengthening the tube at this sec-- tion, the inner surface o said reduced diamo ter section being threaded with the inner edges of the threads and the portions of the tube therebetween iiattened, a iilling oi arc extinguishing material compacted into said threads whereby the voltage breakdown strength along the devious path thus provided between said tube and said arc extinguishing material substantially equals that over the exterior surface of the fuse tube between its ends said filling of are extinguishing having a central bore from the surface of which an arc extinguishing medium is evolved due to the of arc, line terminals at the ends of tube for connection to the circuit and between which recovery voltages are applied, a red-li :e terminal movable through said bore, conducting means :interconnecting said rod-lille terminal and one .of said line terminals, spring means biasing said rodlike terminal toward said one line terminal, the arcing end of said rod-like terminal in the retracted position remaining in said bor-e near one end thereof, conducting means extending from the other line terminal toward said here for a distance several times the length that Vsaid other terr inal is coextensive with said tube, and 4fusible means interconnecting said rod-litre terminal and the last mentioned conducting means and holding the former against the retractile force of said spring means until the same blows `on the occurrence of a predetermined overload in the circuit in which the fuse is connected.

5. In a high voltage fuse tor use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal reduency recovery voltage, in combination, an insulating tube formed of a phenolic condensation product, a fibre liner along the central portion oi said tube for substantially half 'its length to provide increased resistance to internal pressure at this `section and having its inner threaded, a filling of arc extinguishing material having its external surface threaded and interloclred with inner surface oi said fibre liner and. having a bore from the surface of which an arc extinguishing medium is evolved due to the heat' oi an aro, said threaded inner surface of said liner and said are extinguishing material interlo ed therewith providing a devious path therebetween having a substantially greater creepage distance over the juxtaposed surfaces thereof than is provided over the surface of said bo line terminals at the ends of said tube for connection to the circuit and between which said recovery voltages are applied, a rod-like terminal movable through said bore, conducting means interconnecting said rod-like terminal and one of said line terminals, spring means biasing said rod-like terminal toward said one line terminal, the arcing end of said rod-like terminal in the retracted position remaining in said bore near one end thereof, stationary conducting means extending from the other line terminal toward said bore for a distance several times the length that said other terminal is coeXteneive with said tube, and fusible means interconnecting said rod-lilac termina-l and the last mentioned conducting means and holding the former against the retractile force of said spring means until the same 'blows on the occurrence of a predetermined overload in the circuit in which the fuse is connected, said rodlike terminal after release and said conducting means applying voltage stress to the ends of said devious path which because of its greater length as compared to the length of said bore and said arc extinguishing material threaded into said bre liner has a higher voltage break down strength than said bore.

6. In a high voltage fuse for use with electric power systems where:L the transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube formed of phenolic condensation product, a nbre liner along the central portion of said tube for substantially half its length to provide increased resistance to internal pressure at this section, the inner surface of said fibre liner grooved, a filling of arc extinguishing compacted into said grooves whereby the voltage breakdown strength along the devious path thus provided between said liner and arc extinguishing material substantially equals that over the exterior sui'- face of the fuse tube between its ends7 said nlling of arc extinguishing material having a central bore from the surface of which an arc extinguishing medium is evolved due to the heat of an arc, line terminals at the ends of tube for connection to the circuit and between which said recovery voltages are applied, a rod-like terminal movable through said bore, conducting means interconnecting said rod-like terminal and one of said line terminals, spring means biasing said rod-litre terminal toward said one line terminal, the arcing end of said rod-like terminal in the retracted position remaining in said bore near one end thereof, conducting means extending from the other line terminal toward said bore for a distance several times the length that said other terminal is coextensive with said tube, and fusible mea-ns interconnecting said .rod-like terminal and the last mentioned conducting means and holding the former against the retractile force of said spring' means until 'the same blows on the occurrence of a predetermined overload in the circuit in which the fuse is connected.

7. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube having a centrally located arc passageway the diameter of which is substantially less than the internal diameter of the end portions of the tube and a length that is equal to about the sum of the lengths of said end portions, the inner surfaces of said end portions tapering toward the ends of said arc passageway, a terminal at each end of said tube having a tubular extension of conducting material lining the adjacent end portion thereof and having a tapered end portion conforming to the associated tapered section of the tube end portion to distribute substantially uniformly the electrostatic stress incident to circuit interruption, and means for drawing and extending an arc in said passageway.

8. The invention, as set forth in claim 7, wherein the minimum wall thickness of the insulating tube at the tapered section is such that the dielectric strength thereof is equal to at least one half of the flashover value between the terminals over said fuse tube.

9. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery Voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube having the internal central portion for a length substantially equal to half the tube length of reduced diameter to provide increased wall thickness for strengthening the tube at this portion, the inner surface or said reduced diameter portion being threaded, a filling of arc extinguishing material compacted into the threads and having a central bore from the surface f which an arc extinguishing medium is evolved due to the heat of the arc, said bore being located substantially midway the ends of said tube, the end portions o said tube being substantially equal in length and the inner end surfaces thereof tapering toward the ends of said arc passageway, external terminals coextensive with the ends of said tube for connection to the circuit and between which said recovery voltages ar-e applied, a stationary metallic tubular extension from each of said terminals lining the adjacent end portion of said tube for a distance substantially beyond any part of the associated external terminal and having a tapered inner end portion conforming to the associated tapered inner end surface of 1Lhe tube portion to distribute substantially uniformly at each end of said arcing passageway the electrostatic stress incident to circuit interruption, and means within said tube for drawing an arc in said passageway on operation of the interrupter, said metallic extensions acting to distribute electrostatic stress at locations substantially one fourth the length of said tube from each end after interruption of current iiow therethrough and insuring that any restrilsing of an arc between said external terminals will occur in said arcing passageway and not along a path between the former and external to the latter.

l). In a high voltage circuit interrupter for use with electric power systems wherein the 'transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube having external line terminals at its ends for connection to the circuit and between which said recovery voltages are applied, stationary conducting means within said tube extending from each line terminal toward the other for a distance several times the diameter of said tube, the inner surface of said tube between said stationary conducting means being grooved, a lling of granular arc extinguishing material compacted into said grooves and having a central bore from the surface of which an arc extinguishing medium is evolved due to the heat of an arc, and means for drawing an arc in said bore on operation of the interrupter, the length of said bore being suflicient to provide for drawing and extinguishing therein an arc likely t0 be formed on operation of the interrupter, said conducting means acting to distribute voltagey stress applied to said line terminals to prevent arcing therebetween externally of said tube, and said arc extinguishing material compacted in said grooves insuring that the arc between said conducting means will be drawn in said bore.

l1. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube having line terminals at its ends Afor connection to the circuit and between which said recovery voltages are applied, stationary conducting means within said tube extending from each line terminal toward the other for a substantial distance, the inner surface of said tube between said stationary conducting means being threaded, a filling oi arc extinguishing material having a central bore from the surface of which an are extinguishing medium is evolved due to the heat of an arc and having its external surface threaded and interlocked with said threaded inner surface to provide a devious path therebetween having a substantially greater creepage distance over the juxtaposed surfaces than is provided over the surface of said bore, and means for drawing an are in said bore on operation of the interrupter, the length of said bore being sufficient to provide for drawing and extinguishing therein an arc likely to be formed on'operation of the interrupter, said conducting means acting to distribute voltage stress applied to said line terminals to prevent acting therebetween externally of said tube and applying the voltage stress to the ends of said devious path, and said arc extinguishing material in said threads insuring that the arc between said conducting means will be drawn and extinguished in said bore.

12. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery voltage may be substantially greater' than the normal frequency recovery voltage, in combination, an insulating tube having line terminals at its ends for connection to the circuit and between which said recovery voltages are applied, stationary conducting means within said tube extending from each line terminal toward the other for a substantial distance,` a high strength tubular insulating liner between said conducting'means in said insulating tube to provide increased resistance to internal pressure, the inner surface of said liner being threaded, a illing of arc extinguishing material having its surface threaded and interlocked with said inner surface and having a central bore from the surface of which an arc extinguishing medium is evolved due to the heat of an arc, said threaded inner surface of said liner and said arc extinguishing material interlocked therewith providing a devious path therebetween having a substantially greater creepage distance over the juxtaposed surfaces than is provided over the surface ofl said bore, and means for drawing an arc in said bore on operation of the interrupter, the length of said bore being sufficient to provide for drawing and extinguishing therein an arc likely to be formed on operation of the interrupter, said conducting means acting to distribute voltage stress applied to said line terminals to prevent arcing therebetween externally of said tube and applying the voltage stress to the ends of said devious path, and said arc extinguishing material in said threads because the greater length of said devious path as compared to the length of said bore insuring that the arc between said conducting means will be drawn and extinguished in said bore.

13. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery. voltage, in combination, an insulating tube having a centrally located arc passageway the diameter of which is substantially less than the internal diameter of the end portions of the tube and the length of which is equal to about the sum of the lengths of said end portions, the inner surfaces of said end portions tapering toward the ends of said arc passageway, a terminal at each end of said tube having a tubular extension of conducting material lining the adjacent end portion thereof and having a tapered end portion conforming to the associated tapered section of the tube end portion to distribute substantially uniformly the electrostatic stress incident to circuit interruption, the ends of said extensions adjacent the respective ends of said passageway being spaced substantially beyond any other portion of the respective terminal in the direction toward the` other terminal whereby the production of a critical voltage gradient in air adjacent said terminals incident to the drawing and extinguishing of the arc and ashover of the external surface of said insulating tube are prevented, and a contact member movable to and from engagement with one of said tubular extensions through said arc passageway and the other extension.

14. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, an insulating tube having a centrally located arc passageway the diameter of which is substantially less than the internal diameter of the end portions of the tube and the length of which is equal to about the sum of the lengths of said end portions, the inner surfaces of said end portions tapering toward the ends of said arc passageway, a terminal at each end of said tube having a tubular extension of conducting material lining the adjacent end portion thereof and having a tapered end portion conforming to the associated tapered section of the tube end portion to distribute substantially uniformly the electrostatic stress incident to circuit interruption, the ends of said extensions adjacent the respective ends of said passageway being spaced substantially beyond any other portion of the respective terminal in the direction toward the other terminal whereby the projection of a critical voltage gradient in air adjacent said terminals incident to the drawing and extinguishing of the arc and rlashover of the external surface of said insulating tube are prevented, a contact member movable to and from engagement with one of said tubular extensions through said arc passageway and the other extension, and a trailer of insulating material movable with said contact member through said one extension into said passageway whereby any arc between said one extension and said contact member is draw-n in the space between said trailer and said passageway.

15. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, a tubular insulating housing, a lining of arc extinguishing material intimately engaging the inner surface of said housing and providing an arc passagewaywith the space between it and the outer surface of said housing free from voids whereby no path is provided between said housing and liner along which an arc is likely to strike, a terminal at one end of said housing and a contact member movable through the other end of said housing and said passageway for connection tothe circuit and between which said recovery voltages are applied, and an extension from said terminal inside said housing extending to the adjacent end of and in tandem with said passageway for engagement and disengagement bysaid contact member, the end of said extension adjacent said passageway being spaced substantially. beyond any other portion of said terminal in the direction of movement cfsaid contact member to open position whereby the production of a critical voltage gradient in the air adjacent said terminal incident to the drawing and extinguishing of the arc and lashoverv of the external surface of said housing are prevented.

16. The invention, as set forth in the preceding claim, wherein the. lining is formed by la stack of fibre washers having a press t with the innersurface. of the housing.

17. In a high voltage circuit interrupterfor use with electric power systems wherein the transient recovery voltage may be substantially greater than the normal frequency recovery voltage, in combination, a tubular insulating housing, a lining of arc extinguishing material intimately engaging the inner surface of said housing and providing an arc passageway with the space between it and the outer surface of said housing free from voids whereby no path is provided be tween said housing and liner along which an arc is likely to strike, a terminal at one end of said housing and a contact member movable through the other end of said housing and said passageway for connection to the circuit and between which said recovery voltages are applied, an eirtension from said terminal inside said housing extending to the adjacent end oi and in tandem with said passageway for engagement and disengagement by said Contact member, the end of said extension adjacent said passageway being spaced substantially beyond any other portion of said terminal in the direction of movement of said Contact member to open position whereby the production of a critical voltage gradient in the adjacent said terminal incident to the drawing and extinguishing of the aro and flashover of the external surface of said housing are prevented, and a trailer of insulating material movable with said contact member into said passageway whereby any arc between said extension and said contact member is drawn in the space between said trailer and the inner surface of said liner.

18. In a high voltage circuit interrupter for use with electric power systems wherein the transient recovery Voltage may be substantially greater than the normal frequency recovery Voltage, in combination, a tubular insulating housing, a lining of arc extinguishing material intertting closely with the inner surface of said housing and providing an arc passageway, cement intimately bonding said lining to said inner surface of said housing whereby the space between said arc passageway and the outer surface of said housing is free from voids and no path is provided between said housing and liner along which an arc is likely to strike, a terminal at one end of said housing and a contact member movable through the other end of said housing and said passageway for connection to the circuit and between which said recovery voltages are applied, and an extension from said terminal inside said housing extending to the adjacent end of and in tandem with said passageway for engagement and disengagement by said contact member, the end of said extension adjacent said passageway being spaced substantially beyond any other portion of said terminal in the direction of move ment of said contact member to open position whereby the production. of a `critical Voltage gradient in the air adjacent said terminal incident to the drawing and extinguishing of the arc and flashover of the external surface of said housing are prevented.

SIGURD I. LINDELL. CHARLES H. BAKER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,809,013 Rawlins et al Jan. 19, 1943 2,319,276 Triplett May 18, 1943 2,517,624 Baker Aug. 8, 1950 

